But of course the Oreo one is useless, and the cardboard one is flimsy and weak.
So I decided to make a really nice one that shoots M10 hexnuts. Those are very cheap (I buy 100 pcs for five Euros), last forever, and have the right weight. About 10 gramms is ideal for a pump gun, as draw length and weight is limited if you want to be able to fire quickly. I made one a long time ago for 20mm steel balls, but those are too heavy, three time as much as the M10 hexnuts.
Also the weapon is pretty thin, just under 30 mm wide and 80 cm long.
The magazine fits 40 rounds!
The mechanism is really the same as for the Oreo shooter - but I put in a rare earth magnet to hold the "active" nut in place. Nice, you hear a clicking noise when you repeat, and then you know everything's fine.
I have a set of blueprints and also a private how to video online:
See the related post on my forum